This invention relates to remote control operation of a complex apparatus, and more particularly, to a 22 channel remote control receiver operating in the ultrasonic sound spectrum for controlling a television receiver.
Most present day remote control systems for television receivers operate in the ultrasonic frequency range. The ultrasonic signal is typically generated by causing a mechanical hammer to strike a metallic rod which is tuned to be resonant at a certain frequency. The receiver typically utilizes a transducer to convert this ultrasonic sound wave into an electrical signal which is then amplified. The ultrasonic receiver generally contains a number of resonant reed devices each of which is tuned to be resonant at a frequency corresponding to one of the transmitted signals. When one of the transmitter tuned rods is struck it sends out an ultrasonic sound wave of a predetermined frequency which is picked up by the remote control receiver where the corresponding resonant reed is energized. This causes the remote control receiver to execute the desired command. A system like this is quite simple in concept, but is expensive. A great deal of mechanical assembly is required to construct the transmitter tuning rods and hammer mechanisms as well as constructing and individually tuning each of the resonant tuned circuits in the receiver. A system like this is very limited in the number of functions which it can control since only about five tuned rods can be contained in a transmitter case of reasonable size. When changing from channel to channel the user is only able to remotely control either an up command or a down command to the channel changer. For example, to change from channel 5 to channel 10, the user must transmit the up command to sequentially run through channels 6, 7, 8, 9 until arriving at channel 10. This system also has inherent difficulties with preventing randomly generated noise signals from activating the remote control receiver. This is normally circumvented by greatly reducing the sensitivity of the remote control receiver so that only a very strong input signal will cause the remote control receiver to operate. Due to this low sensitivity the user must often transmit the desired command several times or must come closer to the television set to ensure that a sufficient signal strength is received by the remote control receiver.
Some very recently developed remote control systems utilize a continuous wave (C.W.) transmitter capable of generating 15-30 discrete ultrasonic frequencies each of which is able to control a separate function. The difficulty with this system is that each transmitter frequency must be very closely controlled requiring the use of crystals and high accuracy components. Due to the close frequency spacing Doppler shift caused by motion, incorrect commands will be executed if the user moves the transmitter while it is transmitting. Also, since this system has no error checking circuit, it is sensitive to random noise in the ultrasonic range. Noise of this type is often generated by jingling keys on a keychain.